In 2012, Rebekah Fenton gave a lifesaving gift of bone marrow to her younger sister, Elisabeth, who was battling a recurrence of Hodgkin’s lymphoma. On Nov. 9, the sixth anniversary of the transplant...

Almost any schoolchild can tell you: We prevent cavities by brushing our teeth, because that’s how you remove the sticky film containing millions of decay-causing germs.
But this notion is more of an...